FIG. 1 illustrates a perspective view of a known optical transceiver module 2 that has a format known as a small transceiver format. Some examples of known small transceiver formats are the XFP, SFP and SFP+ formats. The transceiver module 2 shown in FIG. 1 is an SFP format transceiver module. The transceiver module 2 includes a metallic module housing made up of an upper metallic housing portion 13 and a lower metallic housing portion 14 that together house a receptacle 5 and a plug 8. The plug 8 receives an optical fiber cable 9 that has a boot 11 attached to an end thereof. The boot 11 includes a ferrule 12 the holds the end of an optical fiber (not shown) of cable 9. A latch 15 of the plug 8 latches the plug 8 to the receptacle 5 to maintain the plug 8 and the receptacle 5 in locking engagement with each other. Features on the upper and lower housing portions 13 and 14 interlock with features on the receptacle 5 to maintain the receptacle 5 in locking engagement with the housing portions 13 and 13.
When the plug 8 is connected with the receptacle 5, the ferrule 12 is contained within the receptacle 5. The receptacle 5 is assembled together with a transmitter package 16 of the transceiver module 2 and the package 16 is fixedly secured to the receptacle 5 opposite the end of the receptacle 5 to which the plug 8 is connected. This is typically referred to as a transistor outline (TO)-can configuration. The transceiver module 2 typically also includes a receiver package (not shown) assembled together with an identical receptacle (not shown) and located inside of the housing portions 13 and 14 beside the transmitter package 16. The transmitter package 16 typically contains a laser diode chip, one or more lenses that make up an optics system, and one or more other electrical components that are all mounted on a submount assembly.
When the plug 8 and transmitter package 16 are secured to the receptacle 5, the end of the optical fiber contained in the ferrule 12 is optically aligned with the optics system (not shown) of the transmitter package 16. Electrical leads 18, 19, 21 and 22 pass through the TO header 17 and communicate electrical signals between traces on the transmitter submount assembly and electrical circuitry (not shown) in the transceiver module 2 that is external to the transmitter package 16. An electrical signal ground 23 on the TO header 17 is used as the signal ground for the electrical components of the transmitter package 16. Other electrical components of the transceiver module 2 that are external to the transmitter package 16 are electrically grounded by connecting their ground contacts (not shown) together and to the signal ground 23 and all together to the upper or lower metallic housing portions 13 and 14, through the metallic receptacle 5. This metallic housing electrical ground connection is referred to as the chassis ground.
In some applications, in order for the transceiver module 2 to operate properly, the signal ground 23 and the chassis ground (not shown) must be electrically isolated from each other. The receptacle 5 is normally made of metal and is in direct contact with the housing portions 13 and 14, which are at the chassis ground potential. Isolating these grounds presents certain challenges that must be addressed, as will be described below with reference to FIG. 3.
FIG. 2 illustrates a perspective view of the receptacle 5 of the transceiver module 2 shown in FIG. 1. The receptacle 5 has a first cylindrical portion 25 shaped to mate with the plug 8 and a second cylindrical portion 27 shaped to mate with the transmitter package 16. Between the first and second cylindrical portions 25 and 27 is a ring defined by a flat cylindrical portion 26A and flanges 26B and 26C. The ring is the part of the receptacle 5 that mechanically mates with mating features of the housing portions 13 and 14. The shape of the ring and its attachment to the housing portions 13 and 14 ensures mechanical and optical alignment of the fiber end contained in the ferrule 12 with the optics system of the transmitter package 16. Because the body of the receptacle 5 is made of metal, the receptacle 5 provides electromagnetic shielding, which is desirable. However, because the body of the ring 26A-26C of the receptacle 5 is normally in physical contact with the upper and/or lower housing portions 13 and 14, electrically isolating the signal ground 23 from the chassis ground, as required by some applications, presents difficulties.
One solution for electrically isolating the receptacle 5 from the housing portions 13 and 14 is to attach the receptacle 5 to the TO header 17 having the transmitter package 16 mounted thereto using some type of isolating resin. Although resins exist that are stable and mechanically resistant, using such a resin during the assembly process tends to be “dirty” because of the possibility that the resin might adhere to optical surfaces of the transmitter package 16. This makes the assembly process more difficult to perform. In addition, the process of attaching the receptacle 5 to the TO header 17 using resin is more difficult to successfully repeat than the laser welding process often used to attach the receptacle 5 to the TO header 17.
Another solution to this problem is to include an isolating cage that surrounds the receptacle and isolates it from the housing. FIG. 3 illustrates a perspective view of a transceiver module 32 having a plastic cage 33 made up of an upper cage portion 33A and a lower cage portion 33B. The cage 33 surrounds the receptacle 35 and prevents the receptacle 35 from coming into contact with the upper and lower metallic housing portions 36 and 37, thereby electrically isolating the signal ground 38 from the chassis ground 39. The transceiver module 32 shown in FIG. 3 is larger than the transceiver module 2 shown in FIG. 1 and is known as an X2 format transceiver module.
Although the plastic cage 33 provides the needed electrical isolation between the signal ground 38 and the chassis ground 39, which is shown for illustrative purposes as being at a location on the lower housing portion 37, the plastic cage 33 is relatively expensive and further complicates the assembly process. More importantly, the cage 33 requires a lot of space in the transceiver module 32. Such a plastic cage generally cannot be used in small format transceiver modules of the type shown in FIG. 1 because there is not enough available space in those types of modules.
Accordingly, a need exists for a way to electrically isolate the signal ground from the chassis ground that is suitable for use in smaller and larger format transceiver modules, which is relatively inexpensive to implement, and which does not further complicate the assembly process.